Question

If two lines intersect, then the vertical angles formed are what?

Answer 1

Let the two lines be:
y = mx + c and y = nx + d, where m not equal n.
Then the angle between them is α, where:
tan(α) = (m - n) / (1 + mn).
When you've calculated α, then calculate 180° - α, since 2 different angles are obviously formed.

So in other words, congruent.

Answer 2

One pair of vertical angles are drawn. They are equal in measure.